Trump's threat against Russia runs parallel to a Senate-led effort to pass crippling sanctions on countries that buy Russian energy.

Trump also revealed that Putin had recently offered to assist in mediating between Israel and Iran during their brief June conflict — an offer he declined. “I said, ‘No, no, you help me get a settlement with you, with Russia,’” Trump recounted. “And I think we're going to be doing that too.”

In response to the escalating threat, President Trump confirmed Monday that the U.S. will send additional Patriot air defense missiles to Ukraine. He noted that the European Union would finance the purchase of what he described as "various pieces of very sophisticated" U.S. weaponry.